Process of softening base bullion



UNITED STATES PATENT GEFIGE.

GEORGE A. MARSH, OF CARNEGIE, PENNSYLVANIA.

PROCESS OF SOFTENING BASE BULLION.

SPECIFICATION forming part of Letters Patent No. 569,293, dated October13, 1896.

A licati filed March 10, 1896. Serial No. 582,615. (No specimens.)

To all whmn it WJ/gl concern.-

Be it known that I, GEORGE A. MARSH, a

citizen of the United States, residing at Car-' negie, in the county ofAllegheny and State of Pennsylvania, have invented or discovered acertain new and useful Improvement in Softening Base Bullion, of whichimprovement the following is a specification.

The invention described herein relates to certain improvements in themethod of softening base bullion preparatory to desilverizin g the same.

The method in most general use consists in maintaining the moltenbullion at a high temperature and allowing currents of air to pass overthe surface of the molten metal, so as to oxidize the impuritiescontained therein. This treatment is carried on until the antimony isreduced to or below six-tenths of one per cent, or to a point where thetreated metal can be advantageously subjected to the action of zinc fordesilverizing. This method of treatment is slow and expensive on accountof the fuel required to maintain the bath for a long period at a hightemperature.

It has been'attempted to hasten the softening operation by introducingsteam into the molten metal, thereby violently agitating the metal andpresenting larger surfaces to the oxidizing action of the air. Thismethod is objectionable, as it is carried below a temperature at whichlitharge can be reduced, so that the large amount of litharge producedremains in the skim and has an injurious effect on the walls of thefurnace and the amount of skim to be worked over is greatly increased.

The antimony and arsenic in the base bullion have been removed by addinglitharge from a cupelling-furnace to the molten metal, which is raisedto such a temperature that a chemical reaction will occur, the oxygen ofthe litharge combining with the arsenic and antimony, forming an oxidthereof, which will be removed with the skim. This method,

while effective in removing the arsenic and antimony, is used only intreating very hard bullion, and will not result in any saving of time orexpense in treating ordinarybullion.

In the practice of my invention the base bullion is melted and raised tosuch a temperature that litharge will be reduced by the arsenic andantimony, such temperature being above the melting-point of litharge andpreferably about a bright-red heat. hen so heated, a pipe is insertedinto the molten metal and a suitable fluid, preferably dry steam, isforced into the metal, producing a violent ebullition and the consequentexposure of large surfaces to the oxidizing action of air. As theelimination of the arsenic and antimony is effected by the reduction oflitharge the molten charge should be maintained at a temperature notless than the meltingpoint of litharge, and preferably at a brightredheat, until the arsenic and antimony have been eliminated as far aspracticable.

The molten charge should be maintained at a temperature not less thanthe melting-point of litharge during the elimination of arsenic andantimony. As soon as the arsenic and antimony have been reduced to orbelow seven or eight per cent. the fire is drawn, the doors of thefurnace are opened for the purpose of cooling the bullion and theadmission of more air for oxidizing the lead, and kept open until thetreatment has been completed. This opening of the doors and consequentcooling of the bullion does not affect the carrying on of the process,as the bullion is and will remain hot sufficiently long to permit of theelimination of the impurities, as hereinafter stated. lVhile it ispreferred to draw the fire and open the furnace-doors when the arsenicand antimony have been reduced to or below seven or eight per cent. as asaving of fuel and time is thereby effected, the doors may be keptclosed and the firing continued until the process of eliminating thearsenic and antimony has been completed. As a result of this operationnot only arsenic and antimony and other impurities are oxidized, but aconsiderable proportion of lead is reduced to litharge.

As the process is carried on at a temperature at which arsenic andantimony will be reacted upon by litharge the formation of the latter isbeneficial for the reason that the litharge will react upon the arsenicand anti mony which have not been previously oxidized by the air, theoxygen of the litharge, combining with the arsenic and antimony, formingan oxid which is removed with the skim. The reactions which occurbetween the litharge, arsenic, and antimony are indicated by thefollowing formulas:

As the result of forming the litha-rge in situ and at such a temperatureand under such conditions as permit of its being reduced by the arsenicand antimony, portions of which are at the same time being oxidized bythe air, the time required for the softening process is greatlyshortened, and as by this process the arsenic and antimony are almostwholly eliminated and in a shorter time than has heretofore beenrequired for a partial elimination the amount of zinc required in thesubsequent desilverizin g process is greatly reduced and subsequentprocesses are shortened, the losses in such processes reduced, and thequality of the refined lead improved.

I claim herein as my invention 1. As an improvement in the art oftreating bullion containing lead, arsenic, antimony, and otheroXidizable impurities, but substantially free from zinc, the methodherein described for removing arsenic, antimony, and other oxidizableimpurities, which consists in melting the bullion, heating the moltenbullion to a temperature at which litharge will be reduced by thearsenic and antimony, 2. 6. about a bright-red heat, and then promotingthe formation of litharge or oxid of lead in the molten bullion by anyknown means of oxidizing, and thereby permitting of the reduction of thelitharge by the arsenic and antimony, and the consequent elimination ofsuch impurities, substantially as set forth.

2. As an improvement in the art of treatin g bullion containing lead,arsenic, antimony, or other oxidizable impurities, but substantiallyfree from zinc, the method herein described for removing the arsenic,antimony, and other oxidizable impurities which consists in melting thebullion, heating the molten bullion to a temperature at which lithargewill be reduced by arsenic and antimony, 2". 6. about a bright-red heat,and then promoting the formation of litharge and other oXids by forcinga fluid into the molten bullion, whereby the molten bullion is agitated,subjecting large surfaces of the metal to the oxidizing action of theair, and opportunity is afforded for the reduction of the litharge bythe arsenic and antimony, substantially as set forth.

3. As an improvement in the art of treating bullion containing lead,arsenic, antimony, and other oxidizable impurities, but substantiallyfree from zinc, the method herein described for removing the arsenic,antimony, and other impurities, which consists in melting the bullion,heating the bullion to a temperature at which litharge will be reducedby arsenic and antimony, t'. 6. about a bright-red heat, promoting theformation of litharge or oXid of lead in the molten bullion by any knownmeans of oxidizing, and thereby permitting of the reduction of thelitharge by the arsenic and antimony, and the consequent elimination ofsuch impurities, and finally subjecting the softened bullion to anysuitable desilverizing process, substantially as set forth.

In testimony whereof I have hereunto set my hand.

GEORGE A. MARSH. lVitnesses DARWIN S. WoLcoTr, M. S. MURPHY.

